Hydrogen peroxide-generating pharmaceutical preparations for the removal of ear wax and the like have been known for many years. According to the U.S. Food & Drug Administration monograph on optic products, ear wax removal formulations must contain 6.5% urea peroxide formulated in an anhydrous glycerine base.
In order to provide maximum peroxide stability, it is generally accepted that it is important to minimize any traces of moisture (water) in the product. However, even with extremely dry glycerine, there is a tendency for decomposition of the product. As the hydrogen peroxide decomposes, it releases oxygen, leaving moisture in the product which further catalyzes decomposition of the peroxide. Thus, there is a need for a stabilizing agent even in the initial absence of moisture.
Manufacturers of currently marketed ear wax removal aid formulations utilize a number of different techniques for stabilizing their products. In addition to urea peroxide and glycerine, one formulation (Murine Ear Drops) lists alcohol, Polysorbate 20 and other ingredients as contents of the product. A second product (Debrox Drops) also contains citric acid, propylene glycol, sodium stannate, water and other ingredients. These additional ingredients are presumably present to enhance product stability.
Many ways of stabilizing urea peroxide have been described in the patent literature. See, for example, U.S. Pat. Nos. 2,259,479; 1,051,926; 1,153,985; 1,210,570; 1,071,186; and 1,040,665. However, the products described in these patents are either insufficiently soluble in anhydrous glycerine base (e.g., sodium phosphate, sodium bitartrate, boric acid, pyrosphosphates, metaphosphates, sodium bisulfate, sodium stannate, etc.), of questionable safety for pharmaceutical use (e.g., phenacetin, tannic acid, benzoylecgonine, protalbic acid, acetanilide, 8-hydroxyquinoline, etc.) or insufficiently effective (e.g., 8-hydroxyquinoline, acetanilide, sodium stannate, etc.) Additionally, some materials such as 8-hydroxyquinoline impart an unacceptable orange color to the product.
It is among the objects of the present invention to provide a new technique for stabilizing glycerine-urea peroxide pharmaceutical solutions, which requires only the use of a single stabilizing ingredient and which may be readily commercially employed to provide solutions useful as ear wax removal formulations having superior stability characteristics.